Testing a tractor 12v generator and regulator

Got a old 1962 mf35, that has old generator/regulator. Short of replacing it with a alternator is there any way to
bypass the regulator to see if the generator works? Generator has a gear built that drives the hour meter cable
so I would like to keep this system, just not sure whats bad, wiring, regulator or generator

To test the generator use a short piece of wire to temporarily ground the generator's Field terminal. If the ammeter shows a strong charge the generator is working.

I think you just ground the field terminal on the generator, and that takes the regulator out of the circuit and the ammeter should read positive and follow RPMs up and down.

Ground the field post on the generator. If it now charges you have a bad regulator section in the voltage regulator.

If it does not charge with field grounded, jumper from generator armature to BAT post on regulator. If it now charges you have a bad cut out relay in the regulator.

If it still does not charge, you have bypassed both sections of the regulator so suspect a generator, ground, or wiring problem.

To check the wiring...

On the regulator, there is a Bat terminal, should have battery voltage at all times. There is a F terminal, should go to the generator F terminal, there is an A terminal, goes to the A or arm terminal of the generator.

To check the generator, engine running at full governed speed, short the F terminal to ground, should get a small spark and the generator go to full charge. Just test, don't leave it grounded.

If grounding the field works, you might get lucky and ease the cover off the regulator, clean the field contacts with a point file (a special thin file made for cleaning contacts) don't use sand paper.

Try to save the original regulator if possible. Much better quality than the new aftermarkets.

If the gen checks bad, open it up, look at the brushes, clean the commutator. Dirty or stuck brushes, dirt dobbers are the usual problem.

If you want to upgrade to an alternator, they can be bought with a tach drive. The price is getting reasonable.

Somewhere on this site is a real good step by step instructions for testing generators. Maybe by johnT?

Good question "is there any way to bypass the regulator to see if the generator works? "

THERE SURE IS if you temporarily dead ground the Gennys FLD post (thereby by passing the VR and its regulation) that creates the max charge condition so if it charges then when running (says genny itself is okay) but NOT otherwise the VR is bad or often its simply not well grounded (or not wired right) so insure it has a good ground first.

You can also check to insure the VR's cutout relay function is operating, it should be open when tractor not running but once the genny produces sufficient voltage it should close so the genny can get connected to and charge the battery. It's essentially between the BAT and GEN/ARM terminal on the VR so if you temporarily jump BAT over to GEN/ARM on the VR while having the gennys FLD post dead grounded THE VR IS BY PASSED so if it charges then the genny is okay so there must be a VR or a wiring or a grounding problem.

For a complete step by step detailed procedure to test the charging system and see if non charging is a genny or a VR problem work through my Troubleshooting Procedure linked below

NOTE BAT on VR wires to load (not battery) side of an ammeter (if it has one)
GEN/ARM on VR wires to gennys FLD post
FLD on genny wires to FLD terminal on VR
VR's case frame needs a good ground as does the gennys case/frame

https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=ttalk&th=2060825

John T
John Ts Charging Troubleshooting

You got it
John Ts Charging Troubleshooting

If you get mad and want to go to an alternator use a 10DN like the MF175 has. This alt uses the same tach drive as the generator. I did this to a MF85.